1. Field of the Invention
This invention relates in general to the field of battery charging devices, and more particularly to multiple battery charging devices for electronic devices and computer systems.
2. Description of the Related Art
Portable computers, personal digital assistants (PDA's), cellular telephones, pagers, calculators, and other such electronic devices are commonplace in today's mobile society. One of the reasons portable electronic devices are so popular is that they provide a user with virtual freedom regarding the location of their use, as long as a source of power is readily available. Although these devices may be powered by plugging them into a standard AC outlet, AC power is often not convenient or readily available. Hence, their real portability and utility comes from their being powered by batteries.
Early portable devices relied on rechargeable lead-acid batteries to provide them with power. However, for some devices such as portable computers, the power requirements were so great that the "on-time" of the device, i.e., the useful battery life between charges, was often measured in minutes, rather than hours. In addition, early rechargeable batteries were inefficient at recharging, having recharge times three to four times that of their useful life. For example, one early portable computer manufactured by the assignee of the present invention had an on-time of approximately 45 to 100 minutes, with a recharge time of approximately 6 to 8 hours. For many users, this amounted to an overnight charge to obtain an hour or so of useful life during the day. What was needed was batteries having faster recharge times. Most rechargeable batteries, typically called battery packs, are made of Nickel Cadmium ("NiCad") or Nickel Metal Hydride ("NiMH"), both of which require a constant current in order to charge. In contrast, the Lithium-Ion ("Li-Ion") battery requires a constant voltage in order to charge. These different types of rechargeable batteries terminate charging under different conditions. The NiCad battery terminates charging upon detecting a negative change in voltage; the NiMH battery detects a temperature gradient; and the Li-Ion battery detects a voltage and has a time-out.
Although there have been tremendous improvements in battery technology, other factors important to the marketplace have developed. Users not only want longer life, with shorter recharge times, they also want to be able to quickly charge two or more batteries at the same time.
One solution to the above-stated problem with quickly recharging two or more batteries was to charge two batteries in the same charging apparatus by independently charging a first battery followed by a second battery. With this solution, a single charging system is used to first recharge the first battery, and when the first battery is completely recharged, the charging system would recharge a second battery. Another solution to the above-stated problem with quickly recharging multiple batteries was to charge each battery in a charging system with its own power line or charging system.
However, both solutions present problems. A problem with the first solution is that it is not efficient. The second solution requires a prohibitive amount of space.
For the foregoing reasons, there is a need for an adaptive multiple battery charging apparatus that allows simultaneous charging of multiple batteries with a single battery charging system.